Recently, the bi-fuel vehicle has been under development for using gasoline and a gas at the same time. As the gas, there are CNG (Compressed Natural Gas) and LPG (Liquid Petroleum Gas). The bi-fuel vehicle is provided with a gasoline fuel system and an LPG fuel system. The bi-fuel vehicle controls the gasoline fuel system and the LPG fuel system with an ECU (engine controller) for selective switching from the gasoline to the LPG or vice versa.
In general, the bi-fuel vehicle drives an engine with the gasoline fuel at the time of starting, and drives the engine with the LPG fuel at the time of running after switching from the gasoline fuel to the LPG fuel.
Manual fuel switching and automatic fuel switching at the time of fuel shortage are available for the bi-fuel vehicle of the gasoline and the LPG at will of a driver of the vehicle.
In general, after noticing a fuel shortage warning, while the driver of a mono-fuel vehicle tends to keep running while risking an engine stop at will of the driver, the driver of the bi-fuel vehicle tends to consume inexpensive LPG to the maximum to a range below which the fuel can be measured.
As a countermeasure for safety on starting off during running, the ECU permits use of LPG only up to a range at which an LPG level sensor can measure an LPG level in the LPG bombe, and then performs automatic fuel switching to gasoline with a slight margin on top of a minimum measurable value into account.
Therefore, use of LPG below the minimum measurable value is not possible by using such a fuel switching control method of the bi-fuel vehicle.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.